Steam generating unit



May 11, 1965 Filed Sept. 23, 1963 A. J. ALIX STEAM GENERATING UNIT FIG.

2 Sheets-Sheet 1 ARTHUR J. ALIX INVENTOR.

May 11, 1965 A. J. ALIX 3,182,639

STEAM GENERATING UNIT Filed Sept. 23, 1963 2 Sheets-Sheet 2 ARTHUR J. ALIX FIG 3 INVENTOR.

United States Patent 3,182,639 STEAM GENERATING UNlT Arthur I. Alix, Worcester, Mass, assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts 7 Filed Sept. 23, 1963, Ser. No. 310,702 4 Claims. (Cl. 122-478) This invention relates to a steam generating unit and, more particularly, to apparatus arranged to generate and to superheat steam for use in a steam turbine for the production of electricity.

It is common practice in steam generating units to superheat the steam by passing it through a series of pendant radiant supenheater platens. These platens are hun g in the furnace in the gas stream in planes parallel to gas How and are spaced apart to obtain the greatest heat pickup by radiation from the hot products of combustion. Platens of this type are used in certain stages of superheat and so the steam that flows through them is near the temperature at which the steam is to be delivered to the turbine. For thermodynamic efficiency the heat absorption should be as high as possible, but the temperature limitation of the tube material determines the possibility of the superheat-er tube withstanding the temperature without failure. The tube material selected is such that the steam temperature in the tubes of the platen is always below the failure temperature of the tubes. However, a difficulty is experienced because of the nesting of the tubes, in that some of the tubes receive greater amounts of heat than others. The temperature of the steam in the outlet header is really an average of the temperatures of the steam from the various tubes and, under conventional practice, this means that the temperature in some of the tube will be greater than the final steam outlet temperature, or, alternatively, the average temperature of the steam at the outlet header must be selected lower than would normally be possible if it could be guaranteed that the temperature of steam in any given tube would not exceed the selected temperature. These and other dificulties experienced with the prior art devices have been obviated in a novel way by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit having a platen superheater in which the temperature in any given tube does not exceed a safe value.

Another object of this invention is the provision of a steam generating unit having radiant type superheatcr in which the temperatures in all of the tubes are close to the desired final super-heat temperature. A further object of the present invention is the provision of a steam generating unit in which radiant superheater loops are so constructed that the outer tube of a given loop is provided with relatively cool steam to prevent failure of the tube.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

A character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view of a steam generating unit embodying the principles of the present invention,

FIG. 2 is an enlarged somewhat schematic view of a portion of the steam generating unit, and

FIG. '3 is a horizontal sectional view of the superheater taken on the line III-HI of FIG. 2.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the steam generating unit, indicated generally by the reference numeral 10, is shown as consisting of a furnace 11 and a boiler 12 3,182,639 Patented May 11, 1965 mounted in a structural steel supporting structure 13. The furnace 11 is shown as having a front wall 14, a rear wall 15, and side walls 16 defining a vertically-elongated rectangular combustion chamber 17. The front wall is provided with an abutment 18 located close to its lower end and provided on its downwardly-directed surface with a burner 19. Similarly, the rear wall 15 is provided with an abutment 21 on the lower surface of which is mounted a burner 22. At its upper end the combustion chamber of the furnace'is provided with a nose 23 extending from the rear wall 15 toward the front Wall and overlying this nose in the rear wall is a gas offtake opening 24. The, opening 24 leads from the combustion chamber 17 to a backpass 25 in which reside a convection superheater 26 and a convection reheater 27. The lower end of the backpass 25 is provided with control dampers 2.8 and is connected through a regenerative air heater 29 to a stack 31.

The output end of the convection super-heater 26 is connected by a pipe 3-2 to an inlet header 33 of a combination convective and radiant superheater 34. This superheater discharges into an outlet header 35 which is connected to a pipe 36 leading to a steam turbine (not shown).

Referring now to FIG. 2, it can be seen that the radiant superheater 3-4 is shown as consisting of a series of steam tubes which, in the preferred embodiment, are twelve in number and which, in the illustrations, have been given alphabetical letters from A to M. Each tube is connected continuously from the inlet header 33 to the outlet header 35 and the tubes are arranged as close as possible to a single plane and consist of three loops 37, 38, and 39. The first and second loops 37 and 38 reside in substantially a single plane, as is evident in FIG. 3, this plane being paraellel to gas flow. The various planes are substantially transversely separated so that gas may flow freely between them. The tubes in the third loop 39 are, however, arranged diagonally across the path of the gases and receive heat in substantial amounts by convection. The superheater 34 is suspended beneath the roof 41 of the furnace 11 and the inlet header 33 and the outlet header 35 reside above the roof 41 out of the flow of gases. Extending above the roof are three supporting members 42, 43, and 44 whose purpose will be clear as the description progresses.

The loop 37 consists of a first leg 45 and a second leg 4.6, the steam flowing first downwardly through the first leg 45 and secondly upwardly through the second leg 46. Similarly, in the normal flow of gas, the gas will pass first over the first leg 45 and then over the second leg 46. On the other hand, in the second loop 38, which is provided with a first leg 47 and a second leg 43, the steam passes first downwardly through the second leg 48, downwardly and then upwardly through the first leg 47. On the other hand, the flow of gas is such as to flow over the first leg 47 first and over the second leg 48 secondly.

The twelve tubes, in connecting the upper end of the second leg 46 of the first loop 37 to the upper end of the second leg 48 of the second loop 38, form a substantial platen 49 extending immediately beneath the roof 41 with the individual tubes arranged parallel thereto. In the third loop 39, the twelve tubes are bent laterally to form only five transverse rows in the first leg 51 and merge to provide four transverse rows in the second leg 52, the second leg extending upwardly for connection to the output header 35.

An interesting feature of the invention is that one of the tubes M is the innermost tube of the loop 37, but becomes the outermost tube of the loop 38. Furthermore, the tube M, instead of joining the other eleven tubes and the platen 49 to progress from the loop 37 to the loop 38, extends upwardly from the second leg 46 of the loop 37 through the roof 41, is bent around the supporting member 42, extends parallel to the upper surface of the roof 41, and is then bent around a supporting member 44 before extending around the outer periphery of the second loop 38. Now, as the tube M passes from the supporting member 42 to the supporting member 44, it is provided with a Y-shaped fitting 53 in the form of a bifurcation having two input legs 54 and 55 and an output leg 56. The tube end is connected to the input leg 55, continues through the fitting and emerges by connection to the output leg 56. The input leg 55', however, is connected to the input header 33 by a tube 57. This tube has a substantially reduced diameter as compared to the tubes in the superheater 34 and ofiers a restriction to the flow of steam from the header 33 to the tube M. The tube M, in leaving the upper end of the first leg 47 of the second loop 38, extends upwardly through the roof 41 again around the supporting member 43, moves downstream to be bent around and carried by the supporting member 44, and then joins the other eleven tubes in forming the third loop 39.

Referring now to FIG. 3, it can be seen that the loops 37 and 38 are restrained to single planes in a direction of gas flow, while the third loop 39 is arranged diagonally of gas flow. An attempt has been made in this drawing to show schematically the manner in which the tubes leaving the top of the first leg 47 of the second loop 38 are connected to the tops of the tubes in the first leg 51 of the third loop 39. For this purpose, two laterally-spaced sets of tubes are shown. As is evident in the drawing, the twelve tubes leaving the first leg 47 of the second loop 38 are broken into approximately three groups to form three diagonal platens making up the third loop 39. As is evident in the drawings, spreading out the tubes in this way causes a substantial convection heat transfer from the gases flowing over the top of the nose 23.

The operation of the invention will now be readily understood in view of the above description. With the operation of the furnace, gases leave the burners 19 and 22 and fiow upwardly through the combustion chamber 17. They pass around the nose 23 and flow horizontally over the top of the nose through the gas oiftake opening 24 into the backpass 25. The steam enters the inlet header 33 from the pipe 32 and flows downwardly in the first leg 45 of the loop 37 and upwardly through the second leg 46. It then flows generally horizontally through the platen 49 to the upper end of the second leg 48 of the second loop 38. From there it flows upwardly through the first leg 47 and then horizontally to the top of the first leg of the loop 39. From the loop 39 it flows into the outlet header 35 and into the pipe 36 for passage to the steam turbine. As is evident, the outer tube of the loops 37 and 38 receive substantially more heat than the other tubes; for one thing, they are continually subject to radiation from many directions instead of only from the sides, as is true of a tube in the center of a platen. For that reason, the outer tube A of the loop 37 becomes the inner tube of the loop 38, so that the average amount of heat it receives is not excessive. On the other hand, the inner tube M of the loop 37 becomes the outer tube of the loop 38. It receives very little heat by radiation when it is the inner tube of the loop 37, so that its steam is relatively cool when it reaches the loop 38. Even so, since the second loop 38 is close to the nose 23, it receives the greatest mass flow of gases of any of the three loops. Because of the action of the nose 23 in throwing the gas forwardly in the combustion chamber, a considerable flow of gas is concentrated over the second loop 38 and despite the precaution of keeping the tube M cool in the first loop, it still would receive a dangerous amount of heat in the second loop. Therefore, relatively cool steam from the inlet header 33 flows through the by-pass tube 57 to the input leg 58 of the fitting 53. Of course, steam through the tube M, which has been the inner tube of the loop 37, also reaches the inlet leg 55 of the fitting; the two steams at different temperatures then pass together through the tube M and are mixed together. The tube 57 is selected small enough to be a substantial restriction and to limit the amount of steam which is thus by-passed.

It can be seen, then, that the outer tube of the second loop, which is generally the most dangerous tube of the entire superheater 34, is provided with steam which is much cooler than any of the other tubes in the superheater. In a practical embodiment of the invention, most of the tubes in the superheater 34 were a conventional one and a half inches in diameter, while the by-pass tube 57 was made as a three-eighth inch outside diameter tube. This meant that approximately 10% to 15% of the steam residing in the tube M (as it passed through the loop 38) was steam originating directl from the inlet header 33.

This means that it is possible by the use of this invention to approach an outlet steam temperature closer to the failure temperature of the tubes, since there is no individual tube which receives an extraordinarily higher amount of temperature of steam than any other.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come Within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 1. A steam generating unit, comprising (a) an elongated combustion chamber having a gas otitake at one end,

(12) a plurality of superheater tube platens residing in the chamber adjacent the gas oiftake so that the products of combustion pass longitudinally over them,

(0) an inlet header mounted outside the chamber and connected to all of the superheater tubes, and

(d) an outlet header mounted outside the chamber and connected to all of the superheater tubes, the inlet and outlet headers being parallel to and spaced from one another, each platen consisting of a first and a second loop and each loop having two legs, the first loop receiving steam from the inlet header and the second loop delivering the steam to the header, one leg of the first loop being directly connected to the inlet header and being located downstream gas-wise of the other leg, one leg of the second loop being connected to the said other leg of the first loop and being located upstream gaswise of the other leg of the second loop, the innermost tube of the first loop forming the outermost tube of the second loop,

(e) a Y-shaped fitting mounted in the tube abovementioned as it passed between the first and the second loop, and

(f) a tube including a restriction connected directly between the inlet header and the fitting.

2. A steam generating unit, comprising (a) an elongated combustion chamber having a gas ofitake at one end,

(b) a plurality of superheater tube platens hanging in the combustion chamber at the said one end and formed in a first and a second loop, the said first loop being located closer to the combustion chamber than the second loop,

(0) an inlet header located outside the chamber to which one end of each superheater tube is connected,

(d) an outlet header located outside the chamber to which the other end of each superheater tube is connected,

(6) means passing at least a portion of the steam in the outside tube of the second loop directly to the second loop from the inlet header,

( and means passing all of the steam in the other tubes of the second loop through the first loop.

3. A steam generating unit as recited in claim 2, wherein the outside tube of the first loop resides inwardly of the second loop.

4. A steam generating unit as recited in claim 2, wherein the innermost tube of the first loop is bent to become the outermost tube of the second loop and receives steam which passes directly from the inner tube through a Y- shaped fitting, the temperature of the said steam being lower than the temperature of the steam that has been exposed to a greater extent to heat in passing through the first upstream loop, thus providing lower temperature steam for the said outermost tube of the second loop, the said outermost tube becoming a supporting tube for the second loop and protecting it from the full efiect of the products of combustion.

References Cited by the Examiner 5 UNITED STATES PATENTS 2,463,888 3/49 Linaker 122479 2,835,479 5/58 Guarraia 122476 

2. A STEAM GENERATING UNIT, COMPRISING (A) AN ELONGATED COMBUSTION CHAMBER HAVING A GAS OFFTAKE AT ONE END, (B) A PLURALITY OF SUPERHEATER TUBE PLATENS HANGING IN THE COMBUSTION CHAMBER AT THE SAID ONE END AND FORMED IN A FIRST AND A SECOND LOOP, THE SAID FIRST LOOP BEING LOCATED CLOSER TO THE COMBUSTION CHAMBER THAN THE SECOND LOOP, (C) AN INLET HEADER LOCATED OUTSIDE THE CHAMBER TO WHICH ONE END OF EACH SUPERHEATER TUBE IS CONNECTED, (D) AN OUTLET HEADER LOCATED OUTSIDE THE CHAMBER TO WHICH THE OTHER END OF EACH SUPERHEATER TUBE IS CONNECTED, (E) MEANS PASSING AT LEAST A PORTION OF THE STEAM IN THE OUTSIDE TUBE OF THE SECOND LOOP DIRECTLY TO THE SECOND LOOP FROM THE INLET HEADER, (F) AND MEANS PASSING ALL OF THE STEAM IN THE OTHER TUBES OF THE SECOND LOOP THROUGH THE FIRST LOOP. 